1. Field of the Invention
The present invention relates to a method for the combustion of coal wherein substantially all of the sulfur content of the coal is retained in the solid effluents and if desired, the resulting gaseous effluents are substantially free of NO.sub.x.
2. Description of the Prior Art
Although coal is by far our most abundant fossil fuel, there are serious problems connected with its use which has prevented it from reaching its full commercial exploitation. Examples of some such problems include problems in handling, waste disposal and pollution. As a result, oil and gas have acquired a dominant position, from the standpoint of fuel sources, throughout the world. This, of course, has led to depletion of proven petroleum and gas reserves to a dangerous level from both a worldwide energy, was well as an economic point of view.
One area in which it is desirable to replace petroleum and gas as an energy source, with coal, is in industries where coal can be burned in combustion devices such as boilers and furnaces. Owing to environmental considerations, the gaseous effluents resulting from the combustion of coal in these devices must be substantially pollution free--expecially with respect to sulfur and nitrogen oxides. Under prior art technology, separate processes were needed to control SO.sub.x and NO.sub.x. SO.sub.x was controlled by wet scrubbing. The cost of wet scrubbing is prohibitive on small installations and excessive on large scale operations. There are also serious operating problems associated with wet scrubbers. NO.sub.x control in the prior art has been achieved by two stage combustion and by post combustion NO.sub.x reduction. The former process involves burning coal in two stages, the first under reducing conditions and the second under oxidizing conditions. Although two stage combustion is both inexpensive and reliable it is believed to have limited effectiveness for control of NO.sub.x and is generally believed to be of no effectiveness for SO.sub.x control. Post combustion NO.sub.x reduction technologies are effective for NO.sub.x, but not for SO.sub.x ; and are generally expensive.